unless flat spin includes considerable motion in a constant direction after the spin is entered.
Translation along the earth axis coordinate system would have been at the wind velocity.
Not claiming a flat spin from altitude, or a flat spin at all, as there are other scenarios. One item to note, if someone can line up the ACARS pieces, is that pitot's are only good for small alphas. On the order of 15 degrees. A flat spin would produce alphas much higher, with rotation, generating a split among all three pitots. If a flat spin is suspected as producing the ASI splits, then it would be left to determine the chances an experienced crew would need to enter the spin in CB turbulence at altitude. Keep in mind that an aircraft at high alpha translates AOA to sideslip with wing rolloff. Two things are needed for spin entry, stall and sideslip.